1. Field of the Invention
The present invention relates to a liquid leakage detector line for detecting the leakage of a liquid such as sulfuric acid, caustic soda, etc., resulting from damages of a transportation pipe line or a storage tank for such liquid.
2. Description of the Prior Art
The present applicant has previously proposed a liquid leakage detector line capable of detecting a wide range of types of liquid leakage, which is used by being installed along a transportation pipe line or a storage tank for such liquid such as sulfuric acid, caustic soda, etc. (Japanese Utility Model Law Application Disclosures SHO 63-57544 to SHO 63-57549). Such a liquid leakage detector line comprises wiry electrodes, consisting of a pair of enamel wires coated with a polyester resin on the conductor for insulation, disposed nearly parallel with each other, and a braided body layer, consisting of at least liquid-absorbent yarn, disposed at the outer periphery of said wiry electrodes.
In such a liquid leakage detector line, leaking liquid such as sulfuric acid, etc. is absorbed by a braided body layer made of liquid-absorbent yarn, and the sulfuric acid, etc. which soaks through the braided body layer dissolves the insulator layer, causing a short-circuit or near short-circuit between a pair of conductors in the wiry electrodes. Thus, detection of leaking liquid is possible by measuring the insulation resistance between the conductors at one end of the liquid leakage detector line. Even when normal rainwater or the like penetrates the liquid leakage detector line, it does not dissolve the insulator layer, and therefore does not cause erroneous actuation.
However, since in a conventional liquid leakage detector line as described above, the insulator layer of the wiry electrode is formed by a so-called enamel coating produced by baking finish of a polyester resin, crazings and cracks can occur during production and laying, due to stress produced inside the insulation layer by external forces applied to the wiry electrodes, such as pressure, tensile force, bending, and the like. As a result, it has been necessary to take a great deal of care during the processes of production and laying, so that external forces do not overly affect the liquid leakage detector line. Such attention is limited, however, and when rainwater and the like seep through the inevitably produced cracks, etc., it creates the problem of erroneous actuation of the liquid leakage detector line. Also, in an enamel coated liquid leakage detector line, the time required for detection of sulfuric acid, etc. is largely dependent on the temperature, and a particular problem occurs when the temperature falls to 15.degree. C. or below, at which the detection time is drastically increased.
In addition, when leakage of liquid is detected, it is necessary to detect the location thereof in order to pinpoint the leakage site and repair it as soon as possible, but there has been no appropriate means of detecting the location of leakage when the area of detection is wide, such as in a liquid leakage detector line along a transportation pipeline for sulfuric acid, etc. For example, a liquid leakage detector line capable of pinpointing the location of leakage is known, wherein a high-resistance wire is constructed along the above mentioned wiry electrodes, whose resistance per unit length is higher than said wiry electrodes (Japanese Patent Application Publication HEI 2-43130), In FIG. 26, X and Y represent a pair of wiry electrodes, and Z represents a high-resistance wire. Each of the resistance values per unit length are indicated by x,y and z, respectively, and each of the near-end terminals are indicated by NX, NY and NZ, respectively. The loop resistance R.sub.xy from N.sub.x to N.sub.y via the location of liquid leakage P, and the loop resistance R.sub.yz from N.sub.y to N.sub.z the same location of liquid leakage P, are measured using a constant-voltage power supply V and an amperemeter A, by which the length L from the near-end to the location of liquid leakage may then be approximated using the following equation. A nichrome wire or the like may be used as the high-resistance wire. EQU L=(R.sub.YZ -R.sub.XY)/(z-x)
The above mentioned liquid leakage detector line is excellent when used as a liquid leakage location detector, but since high-resistance wires are generally rigid, the flexibility and bending resistance of the liquid leakage detector line are reduced. Thus, when installed along a pipeline for sulfuric acid, etc. they are hard to bend and consequently difficult to work with, and if bending is repeatedly forced, the problem of breakage of the high-resistance wires occurs. Further, if for some reason a wiry electrode is broken, detection of liquid leakage becomes impossible at the far end from the breakage site. Rapid detection of the location of breakage and repair thereof is of course necessary, but heretofore there has been no appropriate means of detection of the location of breakage in oases where the area of detection is long. An example of a liquid leakage detector line capable of detection of both the location of leakage and the location of breakage is shown in FIG. 27 (Japanese Utility Model Law Application Publication HEI 2-47539). This liquid leakage detector line possesses a pair of wiry electrodes 3a,3b and a determined number of location detesting insulated element wires 13.sub.1, 13.sub.2 . . . , the wiry electrode 3a is connected with the other wiry electrode 3b, the location detecting insulated element wires 13.sub.1, 13.sub.2 . . . at the far-end terminal, respectively through resistors R.sub.0, R.sub.1 . . . , having approximately the same resistance.
Further, one of the wiry electrodes is divided into specific sections A.sub.1, A.sub.2 . . . , and the points of division P.sub.1, P.sub.2 . . . are cross-connected with the above mentioned location detector insulation coated element wires 13.sub.1, 13.sub.2 . . . for each section. From the near-end terminal, measurement is made of the resistance value between the wiry electrode 3a and the other wiry electrode 3b and the location detector insulation coated element wires 13.sub.1, 13.sub.2 . . . . If this value does not exceed a certain standard value L1, the problem is judged to be a liquid leakage, whereas if the value is equal to or greater than another standard value L2, the problem is judged to be a breakage.
If then, for example, the resistance value between the wiry electrode 3a and a location detector insulation coated element wire 13.sub.1 does not exceed the standard value L1, a liquid leakage is judged to exist in section A1, and if the resistance value between the wiry electrode 3a and a location detector insulation coated element wire 13.sub.2 is equal to or greater than the standard value L2, then a breakage is judged to exist in section A2.
Thus, according to the liquid leakage detector line described in Japanese Utility Model Law Application Publication HEI 2-47539 mentioned above, detection of both leaking sections and broken sections is possible. However, in cases involving detection of liquid leakage from a pipeline for sulfuric acid, etc. which spans a long distance, there must be arranged a large number of sections and consequently a large number of insulation coated wires of the liquid leakage detector line, and the increased number of meters or terminals lowers economic feasibility, while production and operation of the detector line itself becomes more complicated.